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Global Expresss > Apu > Flashcards

Apu Flashcards

1
Q

How do it turn on apu

A

The maintenance/flight crewmember has control over the initiation of the starting and stopping operations of the APU only. The cockpit control for these operations is a single three-position rotary switch on the overhead panel. A second switch on the bleed/air conditioning panel is used to signal APU bleed air.

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2
Q

Where is fadec

A

A full authority digital engine control (FADEC), located on the left side of the aft equipment bay, controls all aspects of APU operation.

The FADEC also provides CAS messages and digital displays of APU-related RPM, EGT and oil tank quantity. In addition, an hourmeter and a startcounter in the APU are activated by the FADEC at 95% RPM during APU starts. Upon shutdown, the FADEC updates the records of the APU time in operation and the total number of starts from these units.

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3
Q

What is red limit

A

106 percent

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4
Q

What is primary purpose for apu

A

Electrical power

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5
Q

What is apu ident

A

The RE220 auxiliary power unit (APU) power plant consists of a single-stage centrifugal compressor, a two-stage axial turbine, an accessory gearbox with an integral oil reservoir, a common shaft to connect the three components above, an annular reverse flow combustor and an exhaust duct and eductor. The power plant is also provided with a monopole and thermocouples to enable measurements of RPM and EGT for display in the cockpit.

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6
Q

Can i operate apu with door open

A

10 mins no load
With loads 5mins

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7
Q

What compressors used

A

The main rotating group of the engine consists of a single-stage centrifugal flow compressor and a two-stage axial flow turbine on a common shaft, which drives an accessory gearbox. The compressor system is equipped with a load control valve (LCV) and a surge control valve. The accessory gearbox drives an AC generator to power the aircraft electrical buses.

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8
Q

Apu operation

A

Engine power is developed through compression of ambient air by a centrifugal compressor. The compressed air, when mixed with fuel and ignited in the annular, reverse-flow combustor, drives a two-stage axial flow turbine. The rotating shaft power of the turbine rotor drives the compressor and the accessory gearbox.

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9
Q

How many start attempts

A

3 then lockout

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10
Q

Where is surge control

A

A surge control air discharge duct is located on the left side of the compartment. It provides an exit port for the APU surge bleed air via the APU surge control valve (SCV). The APU SCV opens only in flight above 15,500 feet.

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11
Q

How is inlet door actuator rigged

A

Through Caims

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12
Q

When does door indication on fadec appear

A

Only if the door position does not agree with Fadec command

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13
Q

What does surge control operate

A

Above 15000ft

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14
Q

What does load control valve do

A

Bleed Air Loads The RE220 can deliver pneumatic power in the form of bleed air from its compressor. The load control valve (LCV) controls the pneumatic load. When this valve is opened, a portion of the compressor discharge air can be directed from the compressor plenum chamber to either the main engine starter or the environmental control system. The LCV opens when the cockpit APU BLEED switch (on the BLEED/AIRCOND panel

overhead) is placed in the OPEN position, or in certain cases, the AUTO position. The engine reaction to bleed air loads is different from its response to shaft loading. Bleed air extraction from the APU diverts pneumatic energy from the turbine as well as some of the cooling air from the combustion system. The latter causes an EGT rise proportional to the rate of air bled.

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15
Q

What is max bleed air alt

A

30000ft

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16
Q

What is max gen altitude

A

37000ft

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17
Q

Max apu gen operatin with reduced elec loading

A

48000ft with reduced elec loading 28.2 kva

18
Q

What is lowest apu oil dispatch

A

3.5qts

19
Q

When can I replace is apu oil

A

15-45 mins from shutdown, can’t do cold

20
Q

Does it have an oil sump heater

A

Yes

21
Q

What can be left on with batt switched off

A

Oil replenishment power, always check

22
Q

How is oil sump heater powered

A

Oil Sump Heater
Figures B5 and B6 A thermostatically controlled, electric resistive, 295-watt element heater is in the gearbox reservoir to heat the oil. The heated oil reduces viscosityinduced drag on the gear train and ensures ease of starting of the APU even after it has been coldsoaked at high altitudes. The heater is powered by aircraft power from AC bus 4, independently of the APU electrical system. The heater has an internal thermostat, which cycles the heater to turn on at 21°C and turn off at 43°C, whether the APU is running or not. The heater only operates in flight and is controlled through the aircraft WOW system.

23
Q

What is de-prime solenoid

A

Deprime Solenoid
Figures B4 and B6 The deprime solenoid is an electronically controlled normally closed, two-way valve located on the lube module. It allows gearbox air to enter the lube pump inlet during APU starts when the oil is cold. The deprime solenoid is located on the left side of the lube module directly behind the oil quantity/temperature sensing unit and is an LRU. The deprime solenoid is energized open during start if oil temperature is less than minus 6.6°C, and is deenergized at starter cutout. When energized open, gearbox air is allowed to enter the inlet of the lube module pressure pump, which reduces starter motor drag during cold-soaked starting conditions. The deprime solenoid is also energized automatically by the FADEC during every shutdown between 60% and 5% rpm.

24
Q

What is;low oil press switch

A

Figures B4 and B6
The low oil pressure (LOP) switch is mounted directly on the gearbox below the starter pad near the aft bearing oil supply port. The switch has a normally closed set of contacts that are opened when oil pressure increases above 40 psig during starts. During ground operation only, if the oil pressure decreases below 30 psig, the LOP switch contacts close. This illuminates the amber CAS message reading APU OIL LO PRESS. After a time delay of 15 seconds, the APU is shut down, followed by the CAS advisory message reading APU SHUTDOWN. During in-flight operation, the APU OIL LO PRESS message is shown with no autoshutdown being performed by the FADEC. During the “APU IN BITE” checks (i.e., during the automatic test performed by the FADEC on all APU electrical/electronic components prior to every start), the LOP switch is checked by the FADEC. On the ground, if this switch is electrically open (above 30 psig), APU starts are inhibited by the FADEC. A fault is logged in the FADEC memory. The above automatic shutdown feature of the APU is inhibited in flight. If the prestart BITE detects a defective LOP switch in flight, the APU will start. This feature allows the APU to operate in flight, i.e., when the APU is in “essential” mode. However, the pilots are informed of the LOP condition by an advisory CAS message reading APU FAULT on the EICAS primary page. They have the option of manually shutting down the APU. The LOP switch is checked by the FADEC during the prestart BITE only and not during APU operation.

25
Q

Oil temp sensor

A

Oil Temperature Sensor
Figures B5 and B6 The oil temperature sensor is located on the front of the gearbox just below the oil pump. It sends an input to the APU FADEC for both minimum oil temperature monitoring and high oil temperature protection. The oil temperature sensor input to the FADEC is checked on power-up. The oil temperature sensor is monitored continuously during operation. Should the oil temperature increase above 148.9°C for 10 seconds on the ground, the APU will shut down. During inflight operation, the APU OIL LO PRESS message is shown with no autoshutdown being performed by the FADEC.

26
Q

How are front and rear bearings lubed

A

Lubrication of Front and Rear Bearings
Figures B7 and B8 Front Bearing Lubrication A duplex type thrust bearing supports the forward part of the rotating group. Its design and mounting arrangement combine to allow minimal axial rotor movement. The sump for this bearing includes the accessory gearbox. Oil is sprayed on the compressor carbon face seal rotor, providing a cooling layer of lubricant to transfer heat from the rotor. Oil is returned to the bottom of the gearbox by gravity alone. The carbon seal forms the primary oil seal during engine operation.

To ensure that engine oil is not lost due to a seal failure, compressor discharge air enters the area behind the face seal. As a result of the above arrangement, a leaking carbon seal would allow air into the oil sump during engine operation, instead of leaking oil out of the sump. Air and any oil, which may leak past the seal on shutdown, is drained overboard by the cavity drain. If any oil seep is noticed through the compressor seal witness drain, it must be concluded that there is an oil leak past the forward carbon seal. The compressor seal witness drain is located on the front of the gearbox. Oil leakage past this seal could cause: • A smell of smoke in the passenger and crew cabins • Progressively higher oil consumption

27
Q

How is rear bearing lubed

A

Rear Bearing Lubrication
The turbine end of the rotating group is supported by a roller bearing in the turbine cavity to allow axial expansion of the APU main shaft. The bearing is lubricated with an oil jet. Return oil is scavenged back to the gearbox by a scavenge element of the oil pump. A piston-ring type of oil seal primarily seals the turbine sump. Buffer air extracted from the Buffered Air Carbon Seal OIL SYSTEM compressor impeller and is routed aft, the chamber forward of the turbine seal becomes pressurized. Any oil leaks would allow the air to enter the sump. The film of buffer air flowing past the seal during APU operation aids in reducing coking of the carbon seal. Oil leak past the carbon seal could cause: • Smoke out of the exhaust tail pipe • Increased oil consumption

28
Q

How is diff press operated

A

Differential Pressure Switches The FADEC monitors the DP at each filter during APU operation. If it detects an impending bypass condition (≥ 35 psid), an APU FAULT advisory message is displayed on the EICAS page. This information is also retained as a record by the FADEC for retrieval by maintenance personnel (through the CAIMS system)

29
Q

When does fadec close fuel valve second atomiser

A

35000ft ???
Secondary flow divider

30
Q

How many amps is starter

A

Supplied from apu direct batt bus 800amp limiter

31
Q

Does starter have clutch

A

Starter and Clutch Assembly Figure D1 The starter motor is designed to rotate and accelerate the APU during the start cycle. The starter is mounted on the gearbox by means of a “V” band clamp. The starter drive shaft engages

the sprag clutch assembly located inside the gearbox. Starter electrical power is provided by the 28-VDC APU battery direct bus. Operation of the starter is automatically controlled through a spring-loaded rotary selector switch marked OFF-RUN-START on the overhead APU panel in the cockpit. When the APU switch on the overhead panel is moved to the momentary START position and released, the FADEC generates a command to engage the starter. Once the APU has reached a self-sustaining speed, the FADEC cuts out the starter power supply. At this point, the sprag clutch mechanically decouples the starter from the gear train. The sprag clutch is mounted in the starter adapter in the accessory gearbox. The sprag clutch assembly bearings and the starter spline drive shaft are lubricated by the APU lubricating system. Both the starter and sprag clutch are LRUs.

32
Q

Where are igniter lugs situated

A

The ignition system consists of a dual output ignition unit, two ignition leads and two igniter plugs. The ignition unit is mounted on the left side of the inlet plenum. The igniter plugs are located at the 2 and 8 o’clock positions on the aft end of the combustor plenum case.

33
Q

How many volts on ign

A

The ignition unit is a dual output, solid-state component. It can operate on 10 to 36-VDC input voltage, and produces a maximum output of 3000 volts. There are two cycles of operation: “burst” for starting and “maintenance” for acceleration. Control of the operation of the ignition system is by inputs from the FADEC.

34
Q

What can kill ref ignition

A

0.2 amp at 3000v

35
Q

What is p2 sensor

A

P2 Sensor
The inlet pressure sensor (P2) is mounted on the upper left corner of the compressor air inlet duct, as viewed from the rear. It senses the air pressure in the APU air inlet duct and changes this pressure to an electrical signal for use within the FADEC. The P2 sensor is a 0 to 15 psia (0-103 kPa) pressure transducer. It acts as a variable resistor when pressure is applied to the diaphragm within, and provides a variable output voltage to the FADEC. It receives a regulated 10-VDC power supply input from the FADEC and generates an output signal of up to 100 mV. The FADEC uses this output for control of circuits that are altitude sensitive.

36
Q

What is T2 sensor

A

T2 Sensor
The inlet temperature sensor (T2) is mounted on the left aft side of the compressor air inlet duct, and senses the temperature of the air entering the inlet duct. The sensor is an electrical resistance temperature device that uses a wire resistance element with an electrical resistance proportional to temperature. This signal is continuous, thus allowing actual temperatures to be monitored during APU operation. The FADEC uses T2 sensor information in conjunction with the P2 sensor input to determine proper fuel schedule.

37
Q

When is your meter powered

A

Above 95 percent and read through Pmat as its an NVM

38
Q

Where is apu start contractor connected to

A

Direct to apu bus

39
Q

What is ASCA

A

Apu start contacted assembly

40
Q

What does ext dc power

A

Only to start apu

41
Q

Where does fadec send its info

A

Dau #3

Global Expresss (28 decks)

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